Abstract

Convective heat transfer can be enhanced by changing flow geometry and/or by enhancing
thermal conductivity of the fluid. This study proposes simultaneous passive heat transfer
enhancement by combining the geometry effect utilizing nanofluids inflow in coils.
The two nanofluid suspensions examined in this study are: water-Al2O3 and water-CuO. The flow behavior and heat transfer performance of these nanofluid
suspensions in various configurations of coiled square tubes, e.g., conical spiral,
in-plane spiral, and helical spiral, are investigated and compared with those for
water flowing in a straight tube. Laminar flow of a Newtonian nanofluid in coils made
of square cross section tubes is simulated using computational fluid dynamics (CFD)approach,
where the nanofluid properties are treated as functions of particle volumetric concentration
and temperature. The results indicate that addition of small amounts of nanoparticles
up to 1% improves significantly the heat transfer performance; however, further addition
tends to deteriorate heat transfer performance.